CN115911176A - Method for improving black silicon absorption rate - Google Patents
Method for improving black silicon absorption rate Download PDFInfo
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- CN115911176A CN115911176A CN202211154782.5A CN202211154782A CN115911176A CN 115911176 A CN115911176 A CN 115911176A CN 202211154782 A CN202211154782 A CN 202211154782A CN 115911176 A CN115911176 A CN 115911176A
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Abstract
The invention provides a method for improving the absorptivity of black silicon, which comprises the following steps: when the current processing line is not the first processing line, placing the material to be processed in an air atmosphere, and cleaning the current processing line by adopting a circular Gaussian spot; after the current processing line is cleaned, the material to be processed is placed in a sulfur hexafluoride atmosphere, and the current processing line is induced by adopting a circular Gaussian spot. The method for improving the black silicon absorption rate can effectively reduce the influence of impurity accumulation on the current processing line and improve the absorption performance of the black silicon.
Description
Technical Field
The invention relates to the technical field of semiconductors, in particular to a method for improving black silicon absorption rate.
Background
The black silicon material can be prepared to improve the absorptivity of the silicon material, and the prepared high absorptivity enables the surface of the silicon material to be black, so the black silicon material is called as black silicon. The existing methods for preparing black silicon include chemical etching, metal-assisted chemical etching, reactive ion etching, laser induction and the like. The ultrafast laser induction method can form a cone structure on the silicon surface to enable incident light to be reflected for multiple times, so that the effective absorption thickness is increased, heavy doping of sulfur atoms is caused, an impurity energy band appears, and the absorption performance of the black silicon material is greatly improved.
In the direct scanning induction process, when the silicon surface is scanned by ultrafast laser, the laser and the silicon material are interacted, the silicon material splashes out from the surface, due to the gravity of a closed chamber, the pressure of sulfur hexafluoride and particles per se, the splashes are accumulated on the silicon surface around a processing area, most of the accumulated matters are silicon oxide, and the induced structure size and the atom doping concentration on the silicon material surface are easily influenced.
Disclosure of Invention
The method for improving the black silicon absorption rate can effectively reduce the influence of impurity accumulation on the current processing line and improve the absorption performance of the black silicon.
The invention provides a method for improving the absorptivity of black silicon, which comprises the following steps:
when the current processing line is not the first processing line, placing the material to be processed in an air atmosphere, and cleaning the current processing line by adopting a circular Gaussian spot;
after the current processing line is cleaned, the material to be processed is placed in a sulfur hexafluoride atmosphere, and the current processing line is induced by adopting a circular Gaussian spot.
Optionally, when the current processing line is the first processing line, the material to be processed is placed in a sulfur hexafluoride atmosphere, and the current processing line is induced by using the circular gaussian light spot.
Optionally, the distance between the current processing row and the previous processing row is 50% -80% of the circular gaussian spot.
Optionally, the current processing line has a plurality of processing points, and each processing point is cleaned by using 100 to 800 laser spots formed by pulses in the cleaning process.
Optionally, the current processing line has a plurality of processing points, and each processing point is induced by a laser spot formed by 200 to 500 pulses in the inducing process.
Optionally, the energy density of the circular gaussian spot in the cleaning process is 0.1-1 times of the energy density of the circular gaussian spot in the inducing process.
Optionally, the energy density of the circular Gaussian spot is 0.1-0.5J/cm2 during the cleaning process.
Optionally, during the induction process, the energy density of the circular Gaussian spot is 0.5-1J/cm2.
Optionally, the gas pressure of the sulfur hexafluoride is not lower than 50KPa.
Optionally, during the cleaning and inducing process, the laser output power is 3W-20W, the frequency is 200-400KHz, the pulse width is below 650nm, and the spot diameter is 30-50 μm.
In the technical scheme provided by the invention, ultrafast laser interacts with a material to generate plasma, the plasma is gasified and ionized in a plasma plume along with the absorption of the laser energy by the plasma, high temperature (> 104K) and high pressure (> 1 GPa) are generated along with the expansion of the plasma, and finally the plasma explodes to generate shock waves and high-temperature airflow, so that the accumulated nano particles are removed. And then, in the sulfur hexafluoride gas atmosphere, a circular Gaussian spot with higher energy is adopted to induce the current path so as to realize the formation of a pointed cone structure and the doping of sulfur atoms. The absorption rate of the black silicon prepared by the technical scheme provided by the invention in the 300nm-2500nm wave band is more than 95%, the absorption rate in the 2500nm-15 mu m wave band is more than 80%, and the absorption performance in the middle infrared wave band is obviously improved.
Drawings
FIG. 1 is a flow chart of a method for improving black silicon absorptivity according to an embodiment of the present invention;
FIG. 2 is a photograph of black silicon prepared by a method of increasing the absorptivity of black silicon according to another embodiment of the present invention;
FIG. 3 is a scanning electron micrograph of a pointed cone structure prepared by a method of improving the absorptivity of black silicon according to another embodiment of the present invention;
fig. 4 is an absorption curve of black silicon prepared by a method for improving the absorptivity of black silicon according to another embodiment of the present invention.
FIG. 5 is a schematic diagram of an apparatus for use in a method of improving the absorptivity of black silicon in accordance with another embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The embodiment of the invention provides a method for improving black silicon absorptivity, which comprises the following steps:
in some embodiments, when the current processing line is not the first processing line, the current processing line forms a deposit of impurities due to the inevitable splashing of material during processing of the previous processing line. In order to avoid the influence of impurity accumulation on the height of an induction structure and the doping concentration of sulfur atoms in the subsequent processing process, in the step, a material to be processed is placed in an air atmosphere, and a circular Gaussian light spot is adopted to clean the current processing line. Because the air atmosphere is in an open environment, the method has a good promoting effect on removing the accumulated impurities, and is favorable for rapidly and thoroughly removing the accumulated impurities. In some preferred embodiments, the current path may be cleaned more than once during the cleaning process in order to remove the accumulated impurities completely. In this embodiment, because of the gravity of airtight chamber, sulfur hexafluoride atmospheric pressure and self particulate matter, will lead to the volume that impurity is piled up great and comparatively concentrated, in order to realize piling up the accurate clearance of impurity, in this embodiment, adopted energy density more to wash for concentrated circular gaussian facula. Meanwhile, the energy of the circular Gaussian spots is mainly concentrated on the left and right of the central area, the effective cleaning range of the circular Gaussian spots is small, and the cleaning effect can be ensured by reducing the distance between adjacent processing lines.
And 200, after the current processing line is cleaned, placing the material to be processed in a sulfur hexafluoride atmosphere, and inducing the current processing line by using circular Gaussian spots.
In some embodiments, after cleaning is completed, impurities accumulated in the current path are cleared, the original surface of the material to be processed is exposed, and then the current path is induced by using a circular gaussian spot, sulfur ions are generated by sulfur hexafluoride under laser in the induction process, and the sulfur ions and the surface of the material to be processed form doping. Under the treatment of the circular Gaussian spots, a pointed conical structure can be formed in the current processing line.
As an alternative embodiment, when the current processing line is the first processing line, the material to be processed is placed in a sulfur hexafluoride atmosphere, and the current processing line is induced by using a circular gaussian spot. In some embodiments, when the current processing line is the first processing line, no previous processing line exists, so that no impurity accumulation is formed on the surface of the current processing line, and at this time, a cleaning step is not required, and the current processing line is directly induced by using the circular gaussian spot.
As an alternative embodiment, the distance between the current processing line and the previous processing line is 50% -80% of the circular Gaussian spot. In some embodiments, because of the high energy density at the center of the gaussian spot and the low energy density at the periphery, to ensure high energy density processing of each region of the material to be processed, processing is performed at a smaller pitch than with a circular gaussian spot.
As an alternative embodiment, the current processing row has a plurality of processing points, and each processing point is cleaned by using 100-800 laser spots formed by pulses in the cleaning process. In some embodiments, the laser processing process typically uses a pulsed laser for processing, i.e., the laser is not continuously irradiated, but is irradiated in portions at an extremely fast frequency. In order to process the material to be processed, in the present embodiment, a plurality of processing sites are provided in each processing line, and each processing site is cleaned by a plurality of pulsed laser spots. In the cleaning process, not only enough energy is provided to clean the accumulated impurities, but also excessive energy is not generated to affect the surface of the material to be treated, so that in the embodiment, each processing point is cleaned by using 100-800 laser spots formed by pulses.
In an alternative embodiment, the current processing row has a plurality of processing points, and each processing point is induced by a laser spot formed by 200-500 pulses during the induction process. In some embodiments, the regularly distributed pointed cone structures are formed on the surface of the material to be processed, which is beneficial to the subsequent cleaning process and maintenance.
As an optional embodiment, the energy density of the circular gaussian spot during the cleaning process is 0.1-1 times of the energy density of the circular gaussian spot during the inducing process. In some embodiments, the cleaning agent is used after cleaningIn the process, the purpose is to cause the ultrafast laser to interact with the material, generating a plasma, where vaporization and ionization occur as the plasma absorbs the laser energy, and high temperatures (b) are generated as the plasma expands (c)>104K) And high pressure (>1 GPa) and finally the plasma explosion generates shock waves and high temperature gas flow, thereby removing the accumulated nano particles. The lower energy density typically required in this process facilitates control of the amount of bulk contaminant removal during the process. In some embodiments, multiple scans may be used to clean the substrate to remove the accumulated impurities. As a preferred embodiment, the energy density of the circular Gaussian spot is 0.1-0.5J/cm in the cleaning process 2 . As a preferred embodiment, the energy density of the circular Gaussian spot in the induction process is 0.5-1J/cm 2 。
In an alternative embodiment, the gas pressure of the sulphur hexafluoride is not less than 50KPa. In some embodiments, the higher pressure atmosphere is favorable for forming high concentration of sulfur ions, and is favorable for doping sulfur ions, and in order to enhance the doping effect, the gas pressure of not less than 50KPa is used in the step. However, a higher pressure gas atmosphere will be detrimental to the cleaning of the deposit, which is also the reason for performing laser cleaning in an open environment such as an air atmosphere in embodiments of the present invention.
As an alternative embodiment, the laser output power used in the cleaning and inducing process is 3W-20W, the frequency is 200-400KHz, the pulse width is below 650nm, and the spot diameter is 30-50 μm.
An exemplary embodiment is provided below to illustrate the technical solution of the present invention:
the embodiment provides a method for preparing black silicon, which is characterized in that an ultrafast laser with the wavelength of 532nm and the pulse width of 400fs is adopted to etch and process a silicon wafer, the laser repetition frequency is 300kHz, the diameter of an acting light spot is adjusted to 40 mu m in a negative defocusing mode, and the processing line spacing is set to 20 mu m. The laser induction parameter can be set to be 1J/cm of light spot energy density 2 The number of the single-point light spots overlapped is 300. LaserThe optical cleaning parameters can be set to be that the energy density of a light spot is 0.3J/cm 2 The number of the single-point overlapped light spots is 200, and the laser cleaning scanning times is 3. The tail gas is output from the tail gas output port and sequentially enters a water tank (the sulfur hexafluoride is slightly soluble) and a poison filtering tank (toxic and harmful substances such as hydrofluoric acid, sulfur dioxide, sulfuryl fluoride, sulfur disulfide, oxygen decafluoride and dust can be effectively adsorbed, and the aim of purification is fulfilled). The processed sample is shown in fig. 2, and it can be seen that the blackening degree of the whole etching area is high, and is obviously contrasted with the surrounding unprocessed silicon material. The microscopic morphology of the processed region was observed by using a scanning electron microscope, and the bulk region was found to be composed of a large number of pyramidal microstructures, as shown in fig. 3, and the height measurements showed that the height of these pyramidal microstructures was all around 10 μm. Finally, the absorption rate of the sample to the 300nm-15 μm wave band is tested, and the result is shown in fig. 4, so that the obtained black silicon sample has good absorption characteristics to the whole test wave band, the absorption rate in the wave band range of 0.3-2.5 μm is more than 97%, and the absorption rate in the wave band range of 2.5-15 μm is more than 86%. In the preparation process of the present embodiment, the apparatus shown in fig. 5 can be used, and in fig. 5, 1 is a laser; 2 is a first reflector; 3 is a second reflector; 4 is a diaphragm; 5 is a third reflector; 6 is a focusing lens; 7 is an SF6 gas input port; 8 is a closed cavity; 9 is polished silicon material; 10 is glass; 11 is a tail gas outlet; 12 is a water tank; 13 is a canister.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. A method of increasing the absorptivity of black silicon, comprising:
when the current processing line is not the first processing line, placing the material to be processed in an air atmosphere, and cleaning the current processing line by adopting a circular Gaussian spot;
after the current processing line is cleaned, the material to be processed is placed in a sulfur hexafluoride atmosphere, and the current processing line is induced by adopting a circular Gaussian spot.
2. The method according to claim 1, characterized in that when the current processing line is the first processing line, the material to be treated is placed in a sulphur hexafluoride atmosphere and the current processing line is induced with a circular gaussian spot.
3. The method of claim 1, wherein the distance between the current processing row and the previous processing row is 50% -80% of the circular gaussian spot.
4. The method of claim 1, wherein the current process row has a plurality of process sites, and wherein each process site is cleaned using 100-800 pulses of laser spots during the cleaning process.
5. The method of claim 1, wherein the current process line has a plurality of process sites, and wherein each process site is induced with 200-500 pulses of laser light spot during the inducing.
6. The method of claim 1, wherein the circular gaussian spot energy density during the cleaning is 0.1-1 times the circular gaussian spot energy density during the inducing.
7. The method of claim 1, wherein the circular gaussian spot has an energy density of 0.1 to 0.5J/cm during the cleaning process 2 。
8. The method of claim 1, wherein the circular Gaussian spot energy density is 0.5 to 1J/cm during the induction process 2 。
9. The method according to claim 1, wherein the gas pressure of said sulphur hexafluoride is not less than 50KPa.
10. The method of claim 1, wherein during the cleaning and inducing, a laser output power of 3W-20W, a frequency of 200-400KHz, a pulse width in the range of 650nm or less, and a spot diameter of 30-50 μm is used.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115475803A (en) * | 2022-09-21 | 2022-12-16 | 中国科学院微电子研究所 | Light trapping structure preparation method |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115475803A (en) * | 2022-09-21 | 2022-12-16 | 中国科学院微电子研究所 | Light trapping structure preparation method |
| CN115475803B (en) * | 2022-09-21 | 2024-03-19 | 中国科学院微电子研究所 | Preparation method of light trapping structure |
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